Last Updated: October 2025

When people think about blood sugar problems, they usually picture diabetes or weight gain. However, unstable blood sugar is also one of the most overlooked root causes of memory loss, brain fog, and even Alzheimer’s disease. At The Carroll Institute in Sarasota, Dr. Garland Glenn, DC, PhD, AFMC helps patients restore brain function by correcting insulin resistance—a metabolic imbalance that can silently starve the brain of fuel.

How the Brain Uses Glucose

Your brain is an energy-hungry organ—it uses about 20% of your body’s total glucose supply. Glucose fuels neurons, allowing you to think, remember, and focus. To use glucose efficiently, your brain depends on a hormone called insulin. Insulin acts as the “key” that opens the cell to allow glucose in.

However, when the body becomes less responsive to insulin—a condition known as insulin resistance—cells struggle to absorb glucose. As a result, blood sugar rises, but the brain doesn’t get the fuel it needs. Over time, this imbalance can lead to sluggish thinking, poor concentration, and, eventually, cognitive decline.

“Type 3 Diabetes”: The Link Between Insulin Resistance and Alzheimer’s

Researchers have begun calling Alzheimer’s disease “Type 3 Diabetes” because of how closely it’s tied to insulin resistance. In fact, studies published in the National Institutes of Health show that metabolic dysfunction can directly impair brain metabolism and increase amyloid plaque buildup.

When insulin can’t do its job, neurons don’t get enough energy. They begin to weaken, lose communication, and eventually die off. This process accelerates memory loss and other Alzheimer’s symptoms. In Dr. Dale Bredesen’s ReCODE research, addressing insulin resistance was a key factor in reversing cognitive decline in over 80% of participants.

How Blood Sugar Imbalance Damages the Brain

• Energy shortage: The brain becomes “fuel-starved,” slowing cognition and reaction time.
• Inflammation: Excess glucose triggers oxidative stress and inflammation in neural tissue. Learn more in Inflammation and the Inflamed Brain.
• Blood vessel damage: High glucose levels weaken blood vessels, reducing oxygen and nutrient delivery.
• Hormone disruption: Insulin resistance often coincides with cortisol and thyroid imbalances, compounding brain fog and fatigue.
• Neurodegeneration: Elevated insulin levels interfere with amyloid clearance, increasing Alzheimer’s risk.

In other words, when blood sugar is unstable, the brain operates in a constant state of stress—like trying to run a high-performance engine on poor-quality fuel.

Signs You May Have Insulin Resistance

• Feeling tired or foggy after eating
• Midsection weight gain or difficulty losing weight
• Frequent sugar or carb cravings
• Afternoon fatigue or “energy crashes”
• High triglycerides or low HDL cholesterol
• Brain fog, memory lapses, or mood swings

Even if you don’t have diabetes, these symptoms may indicate that your cells are no longer responding well to insulin. Identifying and reversing insulin resistance early can protect your brain and overall health for years to come.

Functional Medicine Testing for Metabolic Health

At The Carroll Institute, Dr. Glenn uses advanced laboratory testing to measure fasting glucose, insulin, HbA1c, and other metabolic markers that reveal how your body is managing blood sugar. These data points are combined with cognitive testing to assess how metabolic issues are impacting brain performance.

When needed, additional testing for hormone balance, inflammation, and mitochondrial function helps complete the picture. This allows for a truly personalized plan that addresses the root cause of your brain’s energy imbalance.

Rebalancing Blood Sugar Naturally

Restoring metabolic balance doesn’t require extreme diets or medications in most cases—it requires consistent, evidence-based lifestyle interventions that support the body’s natural rhythm. Dr. Glenn’s protocol includes:

• Low-carbohydrate, anti-inflammatory nutrition: Whole foods and healthy fats support steady energy.
• Intermittent fasting (when appropriate): Improves insulin sensitivity and mitochondrial efficiency.
• Targeted supplementation: Nutrients like magnesium, chromium, and alpha-lipoic acid improve glucose control.
• Hormone optimization: Balanced thyroid and cortisol levels enhance glucose regulation.
• Exercise and movement: Physical activity helps muscles use glucose more effectively.
• Neurorehabilitation: Through Functional Neurology, brain-based exercises improve metabolic regulation and autonomic balance.

Functional Neurology and Brain Metabolism

Beyond nutrition and labs, Dr. Glenn integrates Functional Neurology techniques to improve how the brain controls blood sugar regulation. The autonomic nervous system plays a key role in metabolism—when it’s imbalanced, even healthy habits may not work. Neurorehabilitation helps re-train these pathways, promoting better insulin sensitivity and energy stability.

Additionally, the Neuronic Photobiomodulation Helmet is used to increase mitochondrial efficiency and oxygen delivery to the brain, amplifying the benefits of metabolic healing.

ReCODE and the Metabolic Subtype of Cognitive Decline

Within the Bredesen ReCODE Protocol, insulin resistance is considered one of the major subtypes of cognitive decline. By addressing this metabolic dysfunction early, patients can often reverse brain fog and stabilize memory before permanent damage occurs. When combined with other root-cause strategies—like reducing inflammation and detoxification—results are often profound.

Take the First Step Toward Metabolic and Brain Health

It’s never too early—or too late—to address blood sugar imbalance. Whether you’re experiencing mild cognitive symptoms or just want to protect your brain, improving metabolic health can make a dramatic difference. Book a Discovery Call with The Carroll Institute today to learn how personalized metabolic care can help you regain clarity, focus, and long-term brain resilience.

Sources

• Precision Medicine Approach to Alzheimer’s Disease — NIH (2023)
• Reversal of Cognitive Decline: A Novel Therapeutic Program — NIH (2014)
• Rationale for a Multifactorial Approach to Cognitive Decline — NIH (2022)
• Harvard Health: The Brain and Blood Sugar Connection — Harvard Health Publishing

---